How to redirect the main domain to a sub-domain

To redirect a domain to its own sub-folder,
use the following code in your .htaccess file :

RewriteEngine On
RewriteCond %{HTTP_HOST}%{REQUEST_URI} ^present site.com/$ [NC,OR]
RewriteCond %{HTTP_HOST}%{REQUEST_URI} ^www.present site.com/$ [NC]
RewriteRule ^(.*)$ http://www.present site.com/sub-folder/$1 [r=301,nc]